Thread tension devices



May 24, 1960 E. F. DUNN ET AL 2,937,605

THREAD TENSION DEVICES Filed Feb. 14, 1958 42 W INVENTORS.

Earl F. Dunn, Flg. BY Stanley M. Sliva,

and Francis L. Walling.

ATTORNEY United States Patent 2,937,605 I THREAD TENSION DEVICES Earl F.Dunn, Monroe, and Stanley M. Sliva and Francis L. Walling, Trumbull,Conn., assignors to The Singer Manufacturing Company, Elizabeth, N.J., acorporation of New Jersey Filed Feb. 14, 1958, Ser. No. 715,281

4 Claims. (Cl. 112-254) This invention relates to thread tension devicesfor sewing machines.

It is an object of this invention to provide a novel thread tensiondevice for a sewing machine and more particularly for use with a sewingmachine employing a rotary thread take-up.

It is an object of this invention to provide a thread tensioning unitwith an associated check spring which, when located advantageously on asewing machine, may be properly threaded easily and quickly and withoutdanger of fouling the thread.

The elements which control the needle thread of a lock stitch sewingmachine from a thread supply to the needle include a thread tensioningdevice, a check spring and a take-up. The take-up serves to draw in andgive out thread in accordance with the demands of the stitch forminginstrumentalities; the tensioning device establishes the degree oftension in the thread when all the slack has been taken up, and thecheck spring serves as a small, quick acting auxiliary take-up in whichcapacity it cushions shock loading in the thread and tailors the actionof the main take-up on the thread.

For the most accurate control of the thread the length of thread fromthe tensioning device to the needle should be held to a minimum for thereason that thread has certain inherent elastic properties and theamount that the thread will stretch when tensioned will increase as itslength increases. The shorter the length of thread from the tensioningdevice to the needle, therefore, the more accurate and predictable willbe the control exercized thereon by the take-up.

It is also advantageous in a needle thread control arrangement to attainthe most direct thread path between the tensioning device and theneedle.Since each thread guide and the like, imparts an uncontrolled drag uponthe thread and thus detracts from the effectiveness of the tensioningdevice, an absolute minimum of such thread guides is essential to themost accurate control of the thread tension.

The above considerations as applied to a sewing machine with a rotarytake-up indicate the most advantageous location for the threadtensioning device to be beneath the take-up member, in which position asubstantially complete loop of thread is presented to the take-updirectly from the thread tensioning device and, therefore, the mostdirect and the shortest possible length of thread is attained in thesystem.

When a tensioning device is thus advantageously located beneath a rotarytake-up, however, there arises a difficulty in threading the system.This difiiculty stems from the fact that the manipulations of the threadnecessary to introduce the thread into the check spring from thetensioning unit are substantially identical to those manipulations whichare necessary in order to introduce the thread into the rotary take-up.The thread is apt, therefore, to be engaged on the check spring twice in"ice which case the thread will be snubbed and broken as soon asstitching is attempted.

It is an object of this invention to provide guard means carried as apart of a thread tensioning unit for preventing the double threading ofa check spring.

The above and other objects will be hereinafter more I Fig. 1 representsan end elevational view of a sewing machine bracket arm illustrating arotary take-up mechanism partly broken away and having the threadtensioning unit of this invention applied thereto,

Fig. 2 is an enlarged cross-sectional view of the thread tensioningunit,

Fig. 3 represents an exploded perspective view of the thread tensioningunit, and

Fig. 4 represents a perspective view of the guard member of the threadtension-ing unit.

Referring particularly to Fig. 1 of the drawings a sewing machinebracket arm is indicated at 10 closed at the end by a cover plate 11.Extending outside the cover plate and carried for turning movement withan arm shaft 12 in the bracket arm is a rotary take-up member 13shielded by a take-up guard 14 which extends in spaced relation to thecover plate to define therebetween a thread receiving slot through whicha thread may be introduced to the take-up member.

Journaled for endwise reciprocation in the sewing machine bracket aim isa needle bar 15 carrying a needle 16. A presser bar 17 is also journaledfor endwise movement in the bracket arm and has a presser foot 18secured thereto. A thread guide 19 carried for movement with the presserbar extends through a slot 20 in the cover plate.

Indicated generally at 21 is a thread tensioning unit which includes acheck spring 22. As illustrated in Fig. 1 the tensioning unit is carriedon the sewing machine bracket arm beneath the rotary take-up member andat one side of the thread guide 19. In Fig. 1, a needle thread isillustrated in solid lines in the position it will occupy duringstitching operations, and in phantom lines in two positions A and B thatit will occupy when it is being threaded. The thread after passingthrough the tensioning unit and over the check spring leads through thethread guide 19, over the take-up member 13, through a thread guide 23on the cover plate 11, through a wire thread guide 24 onthe needle bar,and then to the needle.

The constructive features of the sewing machine thus far generallydescribed are conventional and need not be described in further detailfor an understanding of the' present invention.

Referring to Figs. 2 and 3, the thread tensioning unit 21 comprises astud 30 formed at one extremity with external threads 31 and anattenuated slot 32 and at its other extremity with a short slot 33.Secured to thestud 30 i by means of a set screw 34 is a collar 35 formedwith an external annular groove 36 and with a counterbore 37.'

An opening 38 is formed through the side wall of the collar 35 near itsfree end which presents a flat circular.

art these details have not been included in the drawings. Disposed onthe stud 30 flush against the circular face a 39 of the collar 35 is thedisc-likeback portion 41 of a Since 1 guard member 42. Diametricallyopposed lugs 43 struck out from the portion 41 of the guard member seatin the notches 40 of the collar and thus serve to lock the guard memberagainst rotation with respect to the stud. The inside face of the backportion 41 of the guard memher is formed with a raised bearing ring 44which is serrated. Approximately half of the periphery of the backportion 41 of the guard member is formed with a wide flange 45 whichextends substantially parallel to the axis of the stud 30, the remaininghalf of the periphery of the back portion 41 of the guard may beconsidered as coinciding with a gap in the flange 45. A thread entranceslot 46 is formed in the flange 45 and at one end opens into the gap. Atthe other extremity of the flange adjacent the gap, the flange is formedwith a finger 47 which projects outwardly substantially in continuationon the flange.

A disc 48 of frictioning material such as felt, leather, etc., isdisposed on the stud against the bearing ring 44 of the guard member. Athread-engaging wheel 49 is loosely journaled on the stud against thedisc 48. The periphery of the wheel is preferably formed with aplurality of radially extending fingers 50 which are bent outwardlyalternately in opposite directions so as to provide a V-shapedthread-engaging rim for engagement with the thread. A second frictioningdisc 51 identical with the disc 48 is disposed on the stud at theopposite side of the thread-engaging wheel.

A pressure disc 52 is disposed on the stud and formed on the inside facewith a raised serrated bearing ring 53 which bears against thefrictioning disc 51. A pin 54 driven into the pressure disc 52 extendsinto the attenuated slot 32 in the stud so as to prevent rotation of thepressure disc with respect to the stud. The periphery of the pressuredisc is preferably formed with a continuous flange 54 externally taperedinwardly and disposed to overlie the rim of the thread-engaging wheel tocam a thread properly into engagement within the V-shaped rim of thewheel.

A beehive spring 55 is constrained on the stud between the pressure disc52 and a knurled nut 56 on the threads 31 of the stud. The pressureexerted on the thread-engaging wheel between the discs 48 and 51 offrictioning material may be adjusted by means of the knurled nut 56.

Since the guard member 42 and'the pressure disc 52 are both lockedagainst rotation on the stud and the bearing rings 44 and 53 thereonare; serrated, rotation of the frictioning discs 48 and 51 will beprevented and as a result the frictional forces exerted upon the threadengaging wheel will occur from a single source, namely the frictionbetween the discs 48 and 51 and the threadengaging wheel 49. Thefrictioning forces and thus the tension applied to a thread will behighly consistent.

The check spring 22 comprises a series of coils 57 disposed about thestud 30 and within the counterbore 37. An inturned extremity 53 of thecheck spring extends into the short slot 33 of the stud and serves toanchor the check spring thereon. The opposite extremity of the checkspring is formed with a radial arm 59 which extends through the opening38 in the wall of the collar and is bent into a loop 60 which extendsacross the periphery of the guard member 42 in the gap of the flange 45thereon and, therefore, also extends across the rim of thethread-engaging wheel 49. The free extremity 61 of the check spring loop60 is bent to extend substantially parallel to the pressure disc 52 andto a position between the stud 30 and the finger 47 on the guard member.

As illustrated in Fig. l, the thread tensioning unit is preferablysecured to the bracket arm of the sewing machine with the finger 47 ofthe guard member disposed substantially on a line between the stud 30and the axis of turning movement of the rotary take-up member asindicated by the arm shaft 12.

In threading the needle thread control devices of this invention athread limb leading from a supply is grasped by the machine operator anddirected into the thread entrance slot 46 of the thread tensioning unitwhich delivers the thread directly to the rim of the thread engagingwheel. The operator then draws the limb of the thread once around thewheel and into the position marked A" in Fig. l in which the thread hasbeen drawn under the finger 47 and under the free extremity 61 of thecheck spring. Then, holding the thread slightly upwardly inclined, theoperator draws the limb of the thread back, i.e., to the right in Fig.1, the thread being guided by the flange 45 over the check springextremity 61 and under the finger 47. The thread is then drawn under thethread guide 19 after which the thread is drawn upwardly and to the leftto the position marked B in preparation for threading the take up. Fig.1 illustrates how close to the check spring the thread must be drawn inthreading the take-up. In the position marked B, the grasped thread limbwill extend over the finger 47 which will prevent the thread frompassing around the free extremity 61 of the check spring a second time.

The operator then directs the thread into the space between the take-upguard member 14 and the end cover plate 11 to thread the take-up memberand finally threads the guides 23 and 24.

The tensioning device of this invention may thus be threaded quickly andwithout special care on the part of the machine operator and the dangerof fouling the thread by engagement twice with the check spring isminimized.

Having thus described the nature of the invention, what we claim hereinis:

l. A thread tensioning device for a sewing machine comprising a studadapted to be fixed in said sewing machine, thread tensioning means onsaid stud, a guard disc locked against turning movement on said stud atone side of said thread tensioning means, a laterally extending flangeon the periphery of said guard disc arranged to span said threadtensioning means, said flange formed with a gap extending over a portionof the periphcry of said guard disc, a laterally projecting finger onsaid flange at the edge of said gap at check spring anchored on saidstud and extending transversely across the periphery of said guard discin said flange gap, a free extremity on said check spring formed toextend toward said flange and between said laterally extending fingerand said stud.

2. A thread tensioning device for a sewing machine comprising a studadapted to be fixed in said sewing machine, a thread engaging wheeljournaled for turning movement on said stud, means on said stud forimparting a frictional resistance to turning movement of said wheel, aguard disc locked against turning movement on said stud at one side ofsaid thread engaging wheel, a laterally extending flange on theperiphery of said guard disc arranged to span said thread engagingwheel, said flange formed with a gap extending over a portion of theperiphery of said guard disc, said flange formed with a thread receivingslot opening into said gap at one end of said flange and disposedsubstantially in the plane of said thread engaging wheel, a laterallyextending finger formed on said flange adjacent said gap at the oppositeend of said flange, a check spring anchored on said stud and extendingtransversely across the periphery of said guard disc in said flange gap,and a free extremity on said check spring formed to extend substantiallyparallel to said guard disc and between the laterally extending fingeron said guard disc flange and said stud.

3. In a sewing machine having a single bracket arm, a rotary take-up insaid bracket arm, a tensioning unit detachably secured to said sewingmachine bracket arm beneath said rotary take-up member, a threadtensioning device associated with said tensioning unit for impartingfrictional resistance to movement of a thread from a supply to therotary take-up, a check spring anchored on said tensioning unit, a freeextremity formed with a loop on said check spring for engagement with athread extending from the thread tensioning device to said takeup, athread guide, means supporting said thread guide on said sewing machinebracket arm for engagement with the thread extending from the checkspring to the takeup, and a guard member fixedly secured to saidtensioning unit, a finger formed on said guard member and disposedextending across the looped free extremity of said check spring and at apoint substantially between the thread guide and the path of theperiphery of said rotary takerup to prevent double threading of saidcheck spring.

4. In a sewing machine having a bracket arm provided with an end coverplate, a rotary take-up member carried by said bracket arm for movementabout an axis substantially perpendicular to said cover plate, a threadtensioning device comprising a stud fixed in said bracket armsubstantially perpendicular to said end cover plate and beneath saidrotary take-up member, a thread engaging wheel journaled for turningmovement on said stud, means on said stud for imparting a frictionalresistance to turning movement of said wheel, a guard member lockedagainst turning movement on said stud between said thread engaging wheeland said end cover plate, a finger extending from said guard memberoutwardly away from said end cover plate, said finger arranged to spanthe periphery of said thread engaging wheel at a point between the studof said thread tensioning device and the axis of movement of said rotarytake-up member, a check spring anchored on said stud and extendingtransverselyacross the periphery of said thread engaging wheel, and afree extremity on said check spring formed to extend substantiallyparallel to said thread engaging wheel and between said stud and thefinger of said guard member.

References Cited in the file of this patent UNITED STATES PATENTS383,748 Melone May 29, 1888 413,657 Gibbs Oct. 29, 1889 875,610 ParkesDec. 31, 1907 2,462,812 Parry et al. Feb. 22, 1949 2,810,532 Zeier eta1. Oct. 22, 1957 FOREIGN PATENTS 414,717 Italy Aug. 24, 1946

